Ferromagnetic composite coatings on carbon fibers

Alumina- and titania-based composite coatings containing ferromagnetic nanoparticles have been produced on UKN-5000P carbon fibers by an in situ organo-inorganic hybrid sol-gel process using appropriate aqueous metal chloride solutions containing Fe(III) and Co(II). The morphology, phase composition, and elemental composition of the coatings have been studied by high-resolution electron microscopy, X-ray diffraction, and energy-dispersive X-ray microanalysis. The results demonstrate that the oxide coatings containing ferromagnetic nanoparticles are uniform in thickness along and across the fibers and adhere well to the fiber surface. The coatings range in thickness from 100 to 500 nm. In all of the systems studied, the coatings produced on carbon fibers differ in phase composition from powders prepared from identical hydrosols.     

Microstructure of TaC coatings on carbon fibers

This paper examines the possibility of modifying the surface of carbon fibers with tantalum carbide via reactive chemical vapor deposition at temperatures from 800 to 1000°C. We have studied the surface morphology and topography of the coatings on carbon fibers and determined their phase composition by a variety of physicochemical characterization techniques, including X-ray diffraction, high-resolution scanning electron microscopy, and atomic force microscopy. The strength of the modified fibers has been measured at room temperature. The results demonstrate that the coatings are continuous and uniform in thick-ness along and across the monofilaments, with good surface adhesion. The microstructure and surface topography of the coatings depend on the deposition time and temperature.     

Silicon carbide transport during carbothermic reduction of SiO<Subscript>2</Subscript>: Thermodynamic evaluation and experimental study

Mass-transfer processes during the high-temperature carbothermic reduction of silicon dioxide have been studied using thermodynamic modeling. The chemical vapor transport of silicon carbide has been investigated using SiO₂ + xSiC mixtures—major reaction products in the SiO₂-C system—as examples. Thermodynamic modeling results indicate that the vapor transport of silicon carbide is possible at temperatures from 1300 to 1500°C, and that the major gaseous species involved are Si and CO. Vapor transport processes have been studied experimentally. It is shown that the thermal reaction between carbon monoxide and silicon leads not only to direct conversion of silicon particles to silicon carbide but also to the growth of silicon oxycarbide fibers. The synthesized material has been characterized by x-ray diffraction and high-resolution optical microscopy.     

Preparation and characterization of multilayered ZrO<Subscript>2</Subscript> coatings on silicon carbide fibers for SiC/SiC composites

We have studied the surface morphology, phase composition, and oxidation resistance of multilayered tetragonal zirconia coatings produced on silicon carbide fibers by a sol-gel process and measured the tensile strength of individual fibers as a function of the number of layers in the coating. SiC-fiber-reinforced silicon carbide minicomposites have been prepared through pyrolysis of an organosilicon polymer, and their fracture surfaces have been examined. Using microindentation, we have determined the critical fiber-matrix debonding stress. The results demonstrate that the ZrO₂ coating on the fibers has the form of uniform, weakly bonded layers. The presence of a multilayered ZrO₂ interphase alters the fracture behavior of the SiC/SiC composites. The fiber debond stress in the composites markedly decreases with an increase in the number of layers in the interphase.     

Effects of different acetylene/nitrogen ratios on characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition

The effects of C₂H₂/(C₂H₂ + N₂) ratios on the characteristics of carbon coatings on optical fibers prepared by thermal chemical vapor deposition are investigated. The C₂H₂/(C₂H₂ + N₂) ratios are set to 60, 70, 80, 90, and 100%. Additionally, the deposition temperature, working pressure, and mass flow rate are 1003 K, 133 kPa, and 40 sccm, respectively. The deposition rate, microstructure, and electrical resistivity of carbon coatings are measured. The low-temperature surface morphology of carbon-coated optical fibers is elucidated. Experimental results indicate that the deposition rate increases with increasing the C₂H₂/(C₂H₂ + N₂) ratio, and the deposition process is located at a surface controlled regime. As the deposition rate increases, the electrical resistivity of carbon coatings increases, while the ordered degree, nano-crystallite size, and sp² carbon atoms of the carbon coatings decrease. Additionally, the low-temperature surface morphology of the carbon coatings shows that if the carbon coating thickness is not smaller than 289 nm, decreasing the deposition rate is good for producing hermetic optical fiber coatings.     

Fabrication and Properties of MgB2 Coated Superconducting Tapes

We present the formation of MgB₂ coatings by simple and novel aerosol deposition technique which has a potential to escalate towards the fabrication of long superconducting tapes. The thin MgB₂ coatings were produced by using pre-synthesized MgB₂ powder. The ability of this technique to form a precursor powder in a thin film form has greatly reduced the intricacies involved in the synthesis of MgB₂ by other techniques like hybrid physical chemical vapor deposition etc. The as-synthesized thin films were characterized by the x-ray diffraction technique to study the structural properties. The thin films were found to be x-ray amorphous in nature depicting the formation of frustrated structure which showed a superconducting transition onset at around 36 K.     

Nanostructured Pt-γ-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-CeO<Subscript>2</Subscript> catalytic materials and coatings

A new process is described for the suspension synthesis of polycrystalline Pt-γ-Al₂O₃-CeO₂ catalytic materials and coatings, with maltose, C₁₂H₂₂O₁₁, as a reductant and structure former. The process parameters have been optimized in terms of the dispersion medium composition and the way in which Pt is introduced. The coatings are highly uniform in chemical and phase composition, as evidenced by quantitative analysis, optical microscopy, and x-ray microanalysis results. Characteristically, the coatings have a highly porous structure and good adhesive properties. Catalysts prepared by the proposed process show high activity for the oxygen oxidation of CO. The process can be used to fabricate Pt-Pd-Rh catalysts on block supports for the purification of vehicle exhaust gases and industrial off-gases. It has the advantage that high-porosity multicomponent catalytic coatings can be produced on cordierite block supports in a single step.     

Al–O–N and Al–O–B–N thin films applied on Si–O–C fibers

Protective coatings (Al–O–N and Al–O–B–N) on Si–O–C fibers (Tyranno ZMI) were applied in order to enhance oxidation resistance under severe thermo-mechanical conditions in the 400–600 °C temperature range. The coating process consisted in three steps: (i) the transformation of the Si–O–C fiber surface into microporous carbon; (ii) the impregnation of these carbon microporous layers by an aluminium trichloride (AlCl₃) solution and then, (iii) a final heat treatment under ammonia. Processing parameters were studied in order to select the best conditions. Using these conditions, obtained results have shown that coatings were present around each fiber, with a controlled thickness, and that the mechanical properties of the fibers were preserved. Although, these coatings did not entirely stop the oxygen ingress, it has been shown that they strongly reduced the oxidation of the fiber.     

化学镀镍碳纤维/环氧树脂复合材料电磁屏蔽性能

采用化学镀方法对碳纤维进行表面镀镍, 采用SEM、 EDX、 XRD分析了镀镍碳纤维的微观形貌、 镀层成分和镀层结构, 通过电阻测试研究了镀镍碳纤维的导电性。将体积分数为2.5%、 5%、 7.5%、 10%的镀镍碳纤维作为导电填料制备镀镍碳纤维/环氧树脂复合材料, 并用屏蔽室法测试了不同频段复合材料的屏蔽效能。结果表明: 碳纤维化学镀镍后, 表面形成了一层均匀的复合镀层, 镀层中镍的质量分数高达94%, 镀镍碳纤维的电阻值仅为碳纤维原丝的1/54。镀镍碳纤维/环氧树脂复合材料的电磁屏蔽能力较碳纤维原丝有所提高。复合材料的屏蔽效能随镀镍碳纤维添加量的增加而升高。在低频频段(kHz频段), 复合材料的屏蔽能力主要决定于材料的本征参数, 不同镀镍碳纤维含量的镀镍碳纤维/环氧树脂复合材料的屏蔽能力相差不大; 在中高频频段(MHz、 GHz频段), 镀镍碳纤维/环氧树脂复合材料屏蔽效能主要决定于材料的电阻率。     

Characterization and antibacterial performance of ZrCN/amorphous carbon coatings deposited on titanium implants

Titanium (Ti)-based materials have been used for dental/orthopedic implants due to their excellent biological compatibility, superior mechanical strength and high corrosion resistance. The osseointegration of Ti implants is related to their composition and surface treatment. Better biocompatibility and anti-bacterial performances of Ti implant are beneficial for the osseointegration and for avoiding the infection after implantation surgery. In this study, nanocomposite ZrCN/amorphous carbon (a-C) coatings with different carbon contents were deposited on a bio-grade pure Ti implant material. A cathodic-arc evaporation system with plasma enhanced duct equipment was used for the deposition of ZrCN/a-C coatings. Reactive gas (N₂) and C₂H₂ activated by the zirconium plasma in the evaporation process were used to deposit the ZrCN/a-C coatings. To verify the susceptibility of implant surface to bacterial adhesion, Actinobacillus actinomycetemcomitans (A. actinomycetemcomitans), one of the major pathogen frequently found in the dental implant-associated infections, was chosen for in vitro anti-bacterial analyses. In addition, the biocompatibility of human gingival fibroblast (HGF) cells on coatings was also evaluated by a cell proliferation assay. The results suggested that the ZrCN/a-C coatings with carbon content higher than 12.7 at.% can improve antibacterial performance with excellent HGF cell compatibility as well.     

ZrO<Subscript>2</Subscript> coatings on SiC fibers

Zirconia coatings have been produced on Hi-Nicalon fibers via pyrolysis of zirconium oxalates extracted into amine-benzene solutions. X-ray diffraction and electron probe x-ray microanalysis results demonstrate that the pyrolysis of extracts is a viable approach to producing thin zirconia coatings on coreless silicon carbide fibers and that further research is needed to optimize the microstructure of zirconia coatings.     

BN/SiC复合涂层改性炭纤维的吸波性能研究

以尿素、硼酸为原料, 采用浸涂工艺先在炭纤维表面制备BN涂层, 再以三氯甲基硅烷为前驱体, 采用化学气相沉积工艺在纤维表面沉积SiC涂层, 制得了BN/SiC复合涂层改性炭纤维。对BN/SiC复合涂层改性炭纤维的微观结构、抗氧化性能、介电性能及吸波性能进行了研究。结果表明: 炭纤维表面BN涂层的厚度约为0.1 μm, SiC涂层的厚度约为0.7 μm。炭纤维经表面BN/SiC复合涂层改性后, 抗氧化性能明显提高, 开始明显氧化失重温度从560℃提高到790℃, 最终氧化温度从780℃提高到1200℃以上; 且介电性能得到有效改善, 吸波性能显著提高。相比于未改性炭纤维, 厚度为2 mm的BN/SiC复合涂层改性炭纤维的最小反射率减小到-13.3 dB, 小于-10 dB的带宽增加至2.5 GHz。     

Carbon,carbide and silicide coatings

The elements carbon and silicon are the significant constituents of the refractory coating materials discussed in this paper, namely B₄C, pyrocarbon, TiC, SiC, Si₃N₄ and MoSi₂. Because of their hardness and their chemical and oxidation resistance, these materials are of increasing interest as coatings on various substrates. However, their physical and chemical properties limit the number of suitable plating methods. Whilst the CVD technique is the most versatile, the sintering technique is a good alternative, especially if thicker coatings are required.The different coating materials are discussed in detail. The ways in which different coatings can be modified for special applications, e.g. isotropic pyrocarbon coatings for bioengineering purposes, are discussed. Pure silicon carbide and silicon nitride coatings become important as protection against internal oxidation and as barriers in carbon fibre reinforced composites.The problems arising from the simultaneous deposition of two elements to form a specific compound are demonstrated with the examples of SiC, Si₃N₄ and B₄C. The necessity of avoiding chemical reactions with the substrate during deposition is exemplified by the case of TiC coatings on carbon fibres.Finally the technique of preparing metal silicide coatings on refractory metals and carbon by plasma spraying and isostatic hot pressing as protection against oxidation is explained, and the modification of the coatings, in particular to improve thermal cycling behaviour, is discussed.     

Chemical vapour deposition of superconductors

Chemical vapour deposition processes (CVD) can produce metastable fine-grained materials as well as epitaxial coatings and can have a very large throwing power depending on the process parameters. Therefore, CVD is an prospective method to deposit high-temperature superconducting materials withT _c⩾10 K. One of the first superconductors which were produced was Nb₃Sn on tapes and single wires. This superconducting material is, however, today produced by metallurgical methods. Since the detection of Nb₃Ge, CVD has become for these coatings the main method of production for the following reasons: high deposition rates, possibility to dope the material by addition of further doping gases to the CVD-process, continuous process. These coatings were deposited on tapes. For the first time the large throwing power of the CVD process was utilized for the deposition of B1 -NbC _x N _y , on carbon fibre bundles. This opens the possibility to produce multifilamentary structures used for magnetic applications. The structure of the coating can be varied by changing the gas properties, by addition of further gases, by an ultrasonic field, by ignition of a gas discharge and by multi-layering. CVD could also be a prospective method for producing the new class of superconductors withT _c⩾30 K.     

Carbon coatings produced by high temperature chlorination of silicon carbide ceramics

Carbon coatings are widely used to modify surfaces of materials and improve their tribological properties. In this work, carbon layers were formed on various types of sintered and CVD silicon carbide (SiC) using a novel technique involving a reaction with chlorine and chlorine-hydrogen gas mixtures at 1000 °C. Following the work done on powders and fibers, this method successfully produced adherent coatings on SiC ceramics, which could be grown to thickness above 200 μm. Highly disordered carbon with contributions from nanocrystalline graphite was identified by Raman spectroscopy, x-ray diffraction, and energy dispersive spectroscopy. The kinetics of the chlorination reaction at 1000 °C for different gas mixtures fit to a linear reaction rate equation. Coatings produced in pure Cl₂ are graphitic and demonstrate a low hardness (1.8 GPa), Young’s modulus (18 GPa), low wear rate, and a friction coefficient of ∼0.1, which is almost constant for any testing conditions in dry or humid air. Coatings produced in Cl₂/H₂ mixtures have microhardness up to 50 GPa and Young’s modulus up to 800 GPa. Although the presence of hydrogen had little effect on the Raman spectrum of the carbon layers, its presence changed the structure and permeability of the carbon film. Received: 23 April 2001 / Reviewed/Accepted: 24 April 2001     

Microstructure and strength of carbon fibers surface-modified with titanium carbide

Continuous titanium carbide barrier coatings have been grown on UKN-5000 and VMN-4 carbon fibers using chemical vapor transport. The surface morphology and microstructure of as-received and TiC-coated fibers have been studied by scanning electron microscopy. The coating process is shown to raise the tensile strength and Weibull modulus of the fibers. Original Russian Text ? N.I. Baklanova, T.M. Zima, A.T. Titov, T.M. Naimushina, V.P. Berveno, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 162–170.     

Preparation of ZrO2 and ZrO2-Y2O3 coatings on silicon carbide fibers

The formation of ZrO₂ and ZrO₂-Y₂O₃ coatings from hydrous metal oxide sols on Nicalon NLM 202 silicon carbide fibers is investigated in detail. The results indicate that the microstructure of the oxide layer and the surface morphology of the coatings depend on the physicohemical properties of the sol. Kinetic studies of the oxidation of uncoated and coated fibers at different Y₂O₃ contents demonstrate that the oxidation rate of silicon carbide fibers decreases with increasing coating thickness. The effect of oxidation on the phase composition of Nicalon cloth samples coated with ZrO₂ and ZrO₂-Y₂O₃ is examined.     

Physical activation and characterization of multi-walled carbon nanotubes catalytically synthesized from methane

A series of treatment processes were employed to purify and then physically activate the multi-walled carbon nanotubes obtained using catalytic decomposition of methane. In order to characterize and compare the activation effect, the carbon fibers were also treated by the same activation processes. The results showed that the normal physical activation by CO₂ or steam has not too much effect on the surface area of purified multi-walled carbon nanotubes, in particular, the carbon nanotubes were burned when using the poignant activation conditions. However, the surface area of carbon fibers availably etched in the same activation processes is much increased. In addition, the mechanisms of physical activation on multi-walled carbon nanotubes and carbon fibers have been investigated.     

电子束固化树脂基复合材料中碳纤维表面改性研究

利用阳极氧化方法和偶联剂对碳纤维表面的物理和化学性质进行改性，采用原子力显微镜（AFM）和X射线光电子能谱（XPS）分析了碳纤维表面改性前后的形貌和化学成分的变化，利用Keaelble法计算了碳纤维的表面能。研究结果表明，阳极氧化改性的碳纤维表面粗糙度增加，表面活性；表面活性官能闭增多，表面能中极性成分增加明显，碳纤维表面引入的活性氮和化学吸附的碱性物质使电子束固化复合材料界面处的引发剂中毒，复合材料界面性能减弱，与电子束固化工艺相匹配的偶联剂在碳纤维与树脂基体之间形成化学桥，使电子束固化复合材料界面性能得到明显提高。     

Growth of MoS<Subscript>2</Subscript> layers on the surface of multiwalled carbon nanotubes

Molybdenum disulfide has been deposited on the surface of multiwalled carbon nanotubes synthesized through arc vaporization of graphite. As shown by transmission electron microscopy, extended MoS₂ layers have been formed on the surface of the carbon nanoparticles. According to x-ray diffraction results, the crystallinity of the MoS₂ layers in the composites improves with increasing annealing temperature. Free MoS₂ particles can be removed from the composites by centrifugation in bromoform.